I am part of an application that has been utilizing adobe flex for past many years now. The UI has been designed in flex and is fantastic. Lately, however, the application has been switched to an entire set of open source technologies. All the utilities and packages have been gradually moved to their open source counterparts.

Similar activities are planned for flex as well. I was wondering if adobe community can suggest a suitable flex alternative to create a UI layer for a java/j2ee application?

So far we have identified AngularJs (& JavaScript/HTML5)as a suitable replacement for flex and action script. Kindly suggest if there are other open source alternatives that we can look and research on.

Secondly, can anyone please suggest if it is possible to replace Flex with AngularJs and still work with ActionScript? As per my understanding, Flex works with Action Script and AngularJs works well with TypeScript/JavaScript but since I am new in this area, I could be wrong.

because migrate from flex to another technology? It will serve you for many years. Here in the company we are starting a new system and technology used as Front End is the FLEX and do not intend to change.

Apache Flex® is an open source project. You can use IDEs like IntelliJ instead of Adobe Flash Builder.

You are developing a desktop application and not a mobile application?

If you want a modern stack for desktop UI, look at Electron. It's a wrapper around Chromium, and will allow you to use web technologies for UI development. Then, look at ReactJS. It is the most similar to Flex, in that it allows for declarative user interfaces.